As the video says 3" Flowmaster 10 Series, 3" piping, and 4" Cherry bomb twinwall. Personally, I'm in love, not to loud not to quiet, the higher it revs the quieter it gets inside. Minimal drone.
http://www.youtube.com/watch?v=BQhMV5QCFHI
http://www.youtube.com/watch?v=BQhMV5QCFHI